Gods and Fighting Men, by Lady Gregory [1904], at sacred-texts.com
FINN took a wife one time of the Luigne of Midhe. And at the same time there was in his household one Lomna, a fool.
Finn now went into Tethra, hunting with the Fianna, but Lomna stopped at the house. And after a while he saw Coirpre, a man of the Luigne, go in secretly to where Finn's wife was.
And when the woman knew he had seen that, she begged and prayed of Lomna to hide it from Finn. And Lomna agreed to that, but it preyed on him to have a hand in doing treachery on Finn. And after a while he took a four-square rod and wrote an Ogham on it, and these were the words he wrote:
"An alder snake in a paling of silver; deadly nightshade in a bunch of cresses; a husband of a lewd woman; a fool among the well-taught Fianna; heather on bare Ualann of Luigne."
Finn saw the message, and there was anger on hint against the woman; and she knew well it was from Lomna he had heard the story, and she sent a message to Coirpre bidding him to come and kill the fool.
So Coirpre came and struck his head off, and brought it away with him.
And when Finn came back in the evening he saw the body, and it without a head. "Let us know whose body is this," said the Fianna. And then Finn did the divination of rhymes, and it is what he said: "It is the body of Lomna; it is not by a wild boar he was killed; it is not by a fall he was killed; it is not in his bed he died, it is by his enemies he died; it is not a secret to the Luigne the way he died. And let out the hounds now on their track," he said.
So they let out the hounds, and put them on the track of Coirpre, and Finn followed them, and they came to a house, and Coirpre in it, and three times nine of his men, and he cooking fish on a spit; and Lomna's head was on a spike beside the fire.
And the first of the fish that was cooked Coirpre divided between his men, but he put no bit into the mouth of the head. And then he made a second division in the same way. Now that was against the law of the Fianna, and the head spoke, and it said: "A speckled white-bellied salmon that grows from a small fish under the sea; you have shared a share that is not right; the Fianna will avenge it upon you, Coirpre." "Put the head outside," said Coirpre, "for that is an evil word for us." Then the head said from outside: "It is in many pieces you will be; it is great fires will be lighted by Finn in Luigne."
And as it said that, Finn came in, and he made an end of Coirpre, and of his men.